In an internal gear pump (trochoid pump), an outer rotor and an inner rotor having a trochoid tooth profile are hermetically sealed in a casing. The inner rotor and outer rotor, which is fixed to a drive shaft, rotate along with the rotation of the drive shaft and act to suction and discharge liquids. Known examples of this type of pump are described, e.g., in patent documents 1 and 2.
An example of a conventional internal gear pump is shown in FIGS. 6 and 7. FIG. 6 is a perspective view of the assembly of a conventional internal gear pump. FIG. 7(a) is a sectional view of the internal gear pump of FIG. 6, and FIG. 7(b) is a sectional view of an internal gear pump having a different configuration. As shown in FIG. 6, the pump 21 mainly comprises a trochoid 24 in which an inner rotor 23 having a plurality of outer teeth is accommodated inside an annular outer rotor 22 having a plurality of inner teeth. The trochoid 24 is rotatably accommodated in a circular trochoid-receiving recess 25a formed in a flanged cylindrical casing 25. A cover 26 for closing off the trochoid-receiving recess 25a is fixed on the casing 25. As shown in FIG. 7(a), the casing 25 and the cover 26 are securely fastened by bolts 30 on a fixing plate 28 of the device body. The mating faces of the casing 25 and the cover 26 are machined faces that are face-sealed.
The trochoid 24 is configured so that the outer teeth of the inner rotor 23 mesh with the inner teeth of the outer rotor 22 and the inner rotor 23 is rotatably accommodated inside the outer rotor 22 in an eccentric state. Suction-side and discharge-side chambers are formed in accordance with the rotating direction of the trochoid 24 between partitioning points where the rotors are in contact with each other. A drive shaft 31 (not shown in FIG. 6) that is made to rotate by a drive source such as a motor (not shown) passes through, and is fixed, in the axial center of the inner rotor 23. A bearing 32 for supporting the drive shaft 31 is press-fitted into the cover 26. When the drive shaft 31 rotates and the inner rotor 23 rotates, the outer rotor 22 rotates in turn in the same direction as a result of the outer teeth of the inner rotor meshing with the inner teeth of the outer rotor 22. The rotation of the rotors increases the volume, and suctions liquid from an inlet into the suction-side chamber, which is under negative pressure. This suction-side chamber decreases in volume as a result of rotation of the trochoid 24 and is converted to a discharge-side chamber with increased internal pressure. The suctioned liquid is then discharged to the outlet.
A liquid-suctioning nozzle 27 that extends from the casing 25 is provided as necessary on the inlet that communicates with the suction-side chamber (FIG. 7(b)). A metallic or plastic mesh filter 29 for removing foreign matter in the suctioned liquid is installed at a desired location in the inlet pathway leading to the suction-side chamber, including the nozzle 27. The mesh filter 29 is spot-welded or fixed by physical mean such as a C-ring. The mesh filter 29 or the liquid-suctioning nozzle 27 is installed with a rubber packing, etc., interposed to ensure sealing performance.